PROJECT SUMMARY Aflatoxin B1 (AFB1) is a fungal contaminant in food that may be exerting a significant impact on the increasing hepatocellular cancer (HCC) burden in Mexico. HCC epidemiology in Mexico is unusual given the low prevalence of hepatitis virus B and C infection, similar HCC mortality among men and women, and a rural-urban gradient. In Mexico, maize, a staple food, appears to be commonly contaminated by aflatoxins. Thus, AFB1 contamination alone or in combination with non-viral risk factors may be driving HCC incidence rates. We aim to provide initial data on the relevance of AFB1 for HCC in Mexico, while strengthening research capacity for future needs. We specifically will (1) measure circulating AFB1 from 955 women and men from four high HCC burden areas; and (2) create a research network to retrospectively identify aflatoxin-induced mutations in liver samples and determine the feasibility of prospectively obtaining clinical information and biospecimens from incident HCC cases. We will gain insight into HCC risk factors in a population with a unique epidemiological pattern, demonstrate our capacity to access an existing biorepository that will become an important resource for future environmental and cancer research, and create a strong research environment that will foster future collaborative efforts with local, regional, and international scientists.